Download FAQ #2 Alkaline Diet

FAQ #2 Alkaline Diet
SCOPE:
This document aims to provide background information about alkaline diets and cancer,
review evidence on the topic of diet and pH, and provide health care professionals with
information that can be used when discussing this topic with patients or the public.
Background and Rationale:
Proponents of the ‘Acid-Ash diet’ claim that cancer thrives in an acidic environment but
cannot survive in an alkaline environment. Based on this claim some cancer patients will
adjust their diet hoping to slow or stop cancer growth. Foods alleged to make the body
more acidic will be avoided and foods promoting alkalinity are favored.
EVIDENCE:
The pH Scale and pH Regulation in the Body
The pH scale ranges from 0-14. The middle (pH 7) is neutral, numbers below 7 are considered
acidic and numbers above 7 are considered alkaline or basic (Figure 1).
Figure 1. pH Scale
When speaking of the pH of the body one is usually referring to the pH of the blood. The blood
circulates throughout the body to provide nourishment and remove waste for all cells.
The bicarbonate buffering system (described below) maintains the pH of the blood within the
narrow range of 7.35 – 7.45. Changes to the blood pH outside of this range are life-threatening
(Cunningham, 2009).
For healthy individuals, the kidneys play an essential role in maintaining the body’s pH within the
range of 7.35-7.45 by regulating the excretion of hydrogen ions (H+) in the urine. If the pH of the
blood decreases below the normal range, the kidneys will excrete more hydrogen ions (H+) in the
urine to compensate, thus the urine becomes more acidic and the pH of the blood increases
(Whitmire, 2004). When the pH of the blood increases above the normal range (becomes more
alkaline), the kidneys will excrete less H+ in the urine to compensate. This results in less acidic
urine and a decrease in the pH of the blood to its normal range. Thus although blood pH stays
relatively stable, the pH of the urine can fluctuate within the range of approximately 4.5 – 8.5. The
ability of the body to regulate the pH of the blood becomes impaired with individuals with kidney
disease and some respiratory conditions such as COPD and Asthma (Whitmire, 2004).
The pH of the digestive tract varies to aid in chemical digestion. Saliva is slightly acidic with a pH
ranging from 6-7. The stomach produces acid with a pH of approximately 2, the pancreas
secretes bicarbonate with a pH ranging from 8.2-9.3 to neutralize the acidic contents of the
stomach and protect the duodenum as well as provide an optimal pH for pancreatic digestive
enzymes (Gropper, 2013).
Many followers of an alkaline diet test their urine pH to assess the impact of dietary change on
pH. Urine pH will vary depending on variations in the diet, but urine pH does not reflect blood pH
(which needs to be measured by a blood test). Testing urine pH can incorrectly lead people to
believe that they are either acidic or alkaline while serving as a motivator to continue following the
diet pattern and testing (Bonjour, 2013).
Influence of Diet on Blood pH
Classification of foods as either acidic or alkaline comes from research conducted over 100
years ago where a bomb calorimeter was used to determine the calorie content of food (Sherman
& Gettler, 1912). After the food was incinerated the leftover ash was then mixed with water and
the pH was measured. Foods were classified as acid-ash foods and alkaline-ash foods. Acid-ash
foods include white sugar, whole grains, dairy, egg yolk, processed meat, meat, poultry, canned
and packaged snacks and convenience foods, alcohol, and caffeine. Alkaline-ash foods include
vegetables, low-sugar fruit, soybeans, tofu, nuts, seeds, legumes. The term Potential Renal Acid
Load (PRAL) is used to describe the extent that a particular food can impact the acidity of the
urine (Remer & Manz, 1995). Foods with a positive PRAL are likely to make the urine more acidic.
Table 1 describes the PRAL of common foods.
The pH of whole (not incinerated) food does not reflect the pH of the ash it produces (Bonjour,
2013). For example, oranges have a low pH yet produce an alkaline ash.
The acidic or alkaline ash classification system has been stated as evidence for the mechanism
of how diet is proposed to influence the body’s pH by proponents of the alkaline diet. Yet, more
recent research and understanding of principles of chemistry doesn’t fully support the
classification system nor does it account for the buffering systems in the body (Dietitians of
Canada, 2011).
Table 1: Average Potential Renal Acid Load (PRAL) of Common Foods
Food Group
Fats and Oils
Butter
Margarine
Olive oil
PRAL (mEq)
0.6
- 0.5
0.0
Vegetables and Fruit
Asparagus
Carrots
Potatoes
Tomatoes
Spinach
Apple
Banana
Orange
Cherries
Raisins
Grain Productsa
- 0.4
- 4.9
- 4.0
- 3.1
- 14.0
- 2.2
5.5
- 2.7
3.6
- 21.0
Food Group
Beverages
Beer
Red wine
Cola
Meat & Alternatives
Beef
Chicken
Salami
Fish
Lentils
peanuts
Milk & Dairy
products
3.5
Milk
7.0
Hard cheese
6.7
Cottage cheese
Fruit yogurt
a
Includes white, whole wheat and whole grain flours.
Bread
Flour
Noodles, pasta
PRAL (mEq)
- 0.2
- 2.4
0.4
7.8
8.7
11.6
7.9
3.5
8.3
0.7
19.2
8.7
1.2
Cancer and Acidic Environments
Solid tumors create an acidic environment in their surrounding extracellular space due to
upregulation of glycolysis and decreased oxygen (Moellering et al., 2008; Wojtkowiak, Verduzco,
Schramm & Gillies, 2011). Therefore, it is the cancer itself that creates a local acidic environment,
as opposed to thriving because the body or blood is acidic due to food choices or inappropriate pH
regulation by the body. This is in contrast to large scale changes in the pH of the body (blood) as
proposed by the acid-ash hypothesis. While there is evidence that certain eating patterns can
impact the pH of the urine (which is a natural physiological process), consuming a diet of
predominantly acid-ash foods has not been shown to alter the pH of the blood outside of the
range of 7.35-7.45 (Robey, 2012).
CONCLUSION:
Fluctuations in the pH of the urine are a byproduct of pH homeostatis in the body. While
the pH of the urine can fluctuate based on eating patterns, it is not possible to drastically
alter the pH of the body or blood outside of the normal range with diet. The alkaline diet
excludes many high protein choices including meat and dairy foods, and may lead to
inadequate protein intake if these choices are not replaced with other protein-rich options.
It is well established that individuals with cancer have increased protein needs and could
therefore run the risk of not meeting protein requirements. This might cause the body to
use lean tissue (muscle mass) and fat mass to meet its needs and the tumor’s needs,
which is not ideal.
A positive aspect of the alkaline diet is that it does encourage liberal consumption of fruits
and vegetables, which is consistent with public health recommendations for general
health and for individuals with cancer as tolerated.
SPEAKING WITH PATIENTS
Considerations When Speaking with Patients
Patients asking about alkaline diets are likely interested in the relationship between food
and health; they are trying to do what they can to help themselves and likely do not want
to do anything that may cause harm. Each patient may have a different level of
understanding of nutrition and a different interpretation of what it means to eat well.
Patient’s Nutritional Status
Patients at low risk of malnutrition: When a patient is well nourished and able to eat well
and she/he feels strongly about following an alkaline diet despite the lack of evidence to
support this eating pattern, it may be helpful to provide information on protein
requirements and how to meet them. Promoting a plant-based diet is supported by
general health, and cancer prevention and survivorship recommendations. Reducing
feelings of anxiety that anything but complete adherence to a particular eating pattern will
lead to poor outcomes is important and valuable for minimizing food related anxiety and
guilt.
Patients who are malnourished or at risk for malnutrition: When patients believe it is
important to follow an alkaline diet yet are experiencing eating challenges and/or are
struggling to maintain their weight they may resist recommendations to consume foods
and fluids considered to be acidic including high calorie dairy products, canned and
packaged snacks or convenience foods. They may be more receptive to higher calorie
choices more aligned with an alkaline diet such as smoothies made with fruit, nut butters
or smooth tofu, and coconut milk or olive oil.
Responses to Common questions or Statements from Patients:
Patient Question: “I’ve heard that cancer thrives in an acidic environment. Why
wouldn’t following an alkaline diet help to counter this?”
RD Response: Cancer cells produce some acid in their nearby space but this does not
affect the pH of the body as a whole, the blood, or the urine. The premise behind the
alkaline diet is that the pH of the foods we eat can make the pH of the body or blood more
alkaline (less acidic), making it hard for cancer cells to live. However, good quality
evidence shows that pH of the blood is maintained within a very narrow range around
neutral (pH of 7), regardless of the diet. Urine pH can change due to dietary patterns,
which is a normal bodily function.
There are pros and cons to following an alkaline diet:
Following an alkaline diet may not be safe for individuals with cancer. The alkaline diet
limits many high protein foods such as meat and dairy. If these foods are not replaced
with other high protein foods, individuals with cancer may not meet their protein needs,
which can lead to muscle loss.
An alkaline diet does encourage people to eat many vegetables and fruits, which are
healthy choices that many people do not get enough of.
Patient Question: “Why would urine test strips show pH changes based on diet?”
RD Response: Followers of an alkaline diet are often encouraged to test the pH of their
urine as a marker of the pH of their body or blood. Changes in the pH of the urine are
normal and expected and do not reflect the pH of the whole body or blood. This process is
what ensures that the pH of the body (blood) remains very tightly controlled.
Patient Question: “What about alkaline water?”
RD Response: Followers of an alkaline diet are often encouraged to purchase and use
specialized water alkalizers that use a process called electrolysis to alter the pH of tap
water. Alkaline water can contribute to pH changes in the urine in the same way that
alkaline-ash foods may change the pH of the urine. However, drinking alkaline water
cannot change the pH of the whole body or the blood.
Additional Patient-Friendly Resources:
Suzanne Dixon’s blog post titled “Does an ‘Acidic body’ cause or worsen cancer?”
http://nonutritionfear.com/?blogsub=confirming#subscribe-blog (note: readers must scroll
down to find the post)
Canadian Cancer Society. Cancer myths and controversies. An alkaline diet and cancer:
http://www.cancer.ca/en/prevention-and-screening/be-aware/cancer-myths-andcontroversies/an-alkaline-diet-and-cancer/?region=on
American Institute for Cancer Research Blog: http://blog.aicr.org/2010/07/08/anothercancer-and-diet-claim-the-alkaline-diet/
American Institute for Cancer Research:
http://preventcancer.aicr.org/site/News2?page=NewsArticle&id=13441
Created by: Lindsay Van der Meer, RD
Edited by: Andrea Holmes, RD
Reviewed by: Rachel Deschenes
Last modified: January 9, 2015
REFERENCES:
American Institute for Cancer Research (2008). e Newsletter: Cancer and Acid-Base Balance:
Busting the Myth. Retrieved from: http://www.aicr.org/site/News2? page=NewsArticle&id=13441
March 11th 2010.
Bonjour, J. P. (2013). Review article: nutritional disturbance in acid-base balance and osteoporosis:
a hypothesis that disregards the essential homeostatic role of the kidney. British Journal of
Nutrition, 110(7), 1168-1177. doi: 10.1017/S0007114513000962
Cunningham, E. (2009). What Impact Does pH Have on Food and Nutrition? Journal of the
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Dietitians of Canada (2011). Practice-based Evidence in Nutrition [PEN]. Diet Composition –
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Gropper, S. S., & Smith, J. L. (2013). Advanced Nutrition and Human Metabolism (6th edition).
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Medline Plus Medical Encylcopedia – Respiratory Acidosis. Retrieved From:
http://www.nlm.nih.gov/medlineplus/ency/article/000092.htm
Mirkin, Gabe. (2009). Acid/Alkaline Theory of Disease is Nonsense. Retrieved from:
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Moellering, R. E., Black, K. C., Krishnamurty, C., Baggett, B. K., Stafford, P., Rain, M., Gatendby,
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Robey, I. F. (2012). Examining the relationship between diet-induced acidosis and cancer. Nutrition
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Sherman, H. C., & Gettler, A. O. (1912). The balance of acid-forming and base-forming elements
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Trujuillo, E. & Nebeling, L. (2006). Changes in Carbohydrate, Lipid, and Protein Metabolism in
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Oncology Nutrition (pp. 17-27). American Dietetic Association.
Whitmire, S. J. (2004). Water, electrolytes, and acid-base balance. In Mahan, K. L. & EscottStump, S. (11th Eds.) Krause’s Food, Nutrition, & Diet Therapy (pp. 164-179). Philadelphia,
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Wojtkowiak, J. W., Verduzco, D., Schramm, K. J., & Gillies, R. J. (2011). Drug resistance and
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Dietitians of Canada (2011). Practice-based Evidence in Nutrition [PEN]. Diet Composition –
Alkaline Diet Evidence Summary. 2011-04-28; accessed October 7th, 2014.